The present invention relates to improvements in thermoformed plastic containers for food or other articles and particularly to the hinge structure for securing the lid and base of the container together.
Containers for food or other articles thermoformed from plastic material normally comprise a lid and base which are hinged to each other. Such containers are normally thermoformed from a sheet of thermoplastic material by forming in the plastic sheet a base and lid joined to each other by an integral hinge area and forming a crease longitudinally of the hinge area to permit the lid to be folded relative to the base. An example of such prior art container is disclosed in U.S. Pat. No. 5,046,659. This type of hinge is referred to in the art as a full length creased or scored hinge. One of the disadvantages with a hinge of this type is that the lid and base can be easily separated with any torsional pressure. A second type of hinge used in the prior art is known as a full length formed hinge which is usually quite stiff and causes the container to gap open at the ends which can lead to product contamination.
It would be desirable to provide an improved integral hinge structure for a thermoformed plastic container which combines the desirable characteristics of the creased hinge and formed hinge, namely, the tight fit and the torsional strength, while eliminating the undesirable characteristics, namely, the lack of torsional strength and the stiffness of the hinge which causes the container to gap open and leads to product contamination.